1. Field of the Disclosure
The present disclosure is related to the field of piezoelectric materials. More particularly, the present disclosure is related to piezoelectric glass ceramic materials suitable for high temperature applications.
2. Description of Related Art
Piezoelectric sensors and actuators have experienced tremendous growth and wide spread application since the initial work with Pb(Ti,Zr)O3, hereinafter “PZT”, in the early 1950's. Since then, PZT-based piezoelectric devices have dominated the world market. They are widely used in underwater sonar, vibration dampening equipment, medical ultrasound transducers, high frequency buzzers and speakers, fuel injection actuators, and precision positioners. These devices have also been incorporated into “Smart Systems” or “Smart Structures,” utilizing these device's dual nature as both a sensor and an actuator. Some proposed applications are for variable control surfaces or noise/vibration suppression in aerospace and automotive applications.
However, the current temperature limitations of PZT-based devices have restricted these types of applications. The PZT-based devices are limited by the Curie temperature (TC) of these materials; the temperature indicating the complete loss of piezoelectric properties, typically less than 350° C. It is noted, however, that property degradation typically occurs at temperatures lower than the TC, for example, at approximately ½ TC, associated with an irreversible depoling reaction.
Research has not provided a way to increase the Curie temperature (Tc) for PZT-based materials.
Although devices based on PZT materials have been around for over 50 years, as temperature requirements for particular applications continue to rise, more and more standard materials (e.g, PZT materials) simply do not function at these conditions, particularly above 500° C. This particular temperature range, now actively sought by sensor and device manufacturers, is currently the sole domain of select single crystals, e.g., langatate, langasite, GaPO4 and YCOB and its variants.
Ferroelectric ceramics have been pushed to higher temperatures for well over two decades now, but essentially none are functionally useful at temperatures significantly above 500° C. As indicated above, single crystals have been developed that do seem to meet most or all of the requirements, but these single crystals are expensive to produce.
Piezoelectric glass ceramic materials provide an alternative to conventional piezoelectric materials such as PZT ceramics. Since PZT apart from zirconium and titanium contains lead, piezoelectric glass ceramics have a potential to replace PZT as an alternative lead-free material.
U.S. Pat. No. 7,591,961 discloses lithium-based piezoelectric glass ceramic materials Li2O—B2O3—SiO2 that are translucent at least in the visible light range or in the infrared range. U.S. Patent Application Publication No. 2007/0199348 discloses a method of preparing lithium-based piezoelectric glass ceramic materials Li2O—B2O3—SiO2. While these lithium-based piezoelectric glass ceramic materials are functional at ambient conditions, they are not useful at temperatures above 200° C. due to the high mobility of lithium itself.
These lithium-based piezoelectric glass ceramic materials are not deemed useful for high temperature applications because of their sensitivity to thermal changes, and are not competitive with existing high temperature materials. Therefore, because of these property deficiencies, the lithium-based piezoelectric glass ceramic materials are not considered viable candidates for high temperature applications for state-of-the-art, technically demanding material fields.